1. Physicochemical aspects of the choice of silicon-bearing binders for production of refractories

The principles for selecting a silicon-bearing binder for refractory production are considered. The effect of the heat treatment temperature on the crystallization of SiO₂ gels with various prehistories is considered. It is shown that ethyl silicate binders have an advantage over other silicon-bearing binders that consists in that SiO₂ gel obtained from ethyl silicate éTS-32 can retain the amorphous state upon heating to over 1273 K. Translated from Ogneupory i Tekhnicheskaya Keramika, Nos. 1–2, pp. 8–11, January–February, 1999.     

A novel method for the hydrolysis of ethyl and isopropyl silicates

The hydrolysis of ethyl and isopropyl silicates without the use of an acid or base catalyst is described. The silicate and an alcohol which is a mutual solvent for water and the silicate are treated with water, preferably under reflux. For ethyl silicate the reaction temperature can be as low as 40°C. A liquid hydrolysate is obtained when the rate of water addition is carefully controlled. This hydrolysate will form a rigid coherent gel capable of binding refractory materials. Liquid hydrolysates prepared in this way have been used to make refractory shapes, also foundry moulds and cores for precision piece moulding work and an ethyl silicate hydrolysate can be used to prepare an anti-corrosion paint based on zinc. It would be expected that other lower alkyl silicates can be treated similarly to form hydrolysates which give a rigid coherent gel capable of binding refractory materials and which can also be used to prepare anti-corrosion paints based on zinc.     

Low-temperature synthesis of SiC in heat-treatment of gels of hydrolyzed ethyl silicate

The problem of low-temperature synthesis of -SiC in heat treatment of gels of hydrolyzed ethyl silicate is considered. Data obtained in DTA, IR, Raman spectroscopy, and EPR physicochemical investigations of the process of gel transformation in heat treatment in air are presented. A mechanism of the organization of the carbon system in a gel and possible ways of synthesizing SiC at low temperatures are suggested. Synthesis of SiC in heat treatment of gels of ethyl silicate at a rate exceeding 10 K/min is established by the x-ray method beginning with 773 K.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 9, pp. 14 – 19, September, 1996.     

Preparation of Silica Fillers for Stomatologic Composite Materials

Colloidal chemical processes in ethyl silicate gels and the crystallization of heat-treated silica are studied. The ethyl silicate/water ratio is shown to affect the optical properties of the filler. The effect of modifying additives on the refraction of light of heat-treated silica gel powders is studied. Controlled addition of Al₂O₃makes it possible to obtain powders with the required value of refraction index in the range of 1.490 – 1.510 to within 0.01.     

Preparation and properties of some acyloxysilanes

Acyloxy derivatives of silicon were prepared by the interchange reaction between carboxylic acids (including various grades of palmitic acid) and tetraethoxysilane, and by the interchange reaction between palmitic acid and technical ethyl silicate (silica content 40%) or technical isopropyl silicate (silica content 38%). In most of the reactions, sodium methoxide was used as catalyst. Some physical properties of the reaction products were determined, and the materials made from palmitic acid were evaluated as water-repellent coatings on cotton cloth.     

GC/MC法分析正硅酸乙酯

用气相色谱法对样品进行分析，得到了四个完全分离的色谱峰。采用色／质联用技术(GC／MC)确定这四个峰分别为乙醇、正硅酸乙酯、二聚硅酸乙酯、三聚硅酸乙酯，并测定了它们的相对含量。     

Structure Control of Calcium Silicate Hydrate Gels for Dye Removal Applications

The structure of calcium silicate hydrate (C‐S‐H) gels was modified by hydrothermal reaction with aqueous acetic acid solvent, and then the C‐S‐H gels were used for dye removal from aqueous solution. With increasing acetic acid concentration, the Ca:Si molar ratio decreased and the length of the silicate anion chain structure of the C‐S‐H gels increased. The silicate anion chain length affects the number of available silanol groups on the surface of the C‐S‐H gel: the longer the silicate anion chain length, the greater the number of negative charges and the higher the surface potential. C‐S‐H gels with a long silicate anion structure exhibited higher adsorption capacity for methylene blue than gels with a short silicate anion structure. The enhanced adsorption capacity of the C‐S‐H gels is related to the higher number of silanol groups in the bridging silica tetrahedra of the intermediate anion chain structure compared with those in the end units of silica tetrahedra.     

Silicone polymers in oxide refractories technology

Conclusions We developed a method for obtaining silicone bonds for refractory materials based on nonhydrolyzed ethyl silicate, silicone resins, and organic adhesive component.Using corundum and periclase refractories as examples we demonstrated that use of the new bonds contributes to a significant strengthening of the materials in the range 20–900°C, and they are therefore prospective for preparing unfired refractories. The use of bond ensures densification and strengthening of corundum refractories, while simultaneously reducing the shrinkage, and leads to an increase in the stabilization of the high-temperature strength of the articles and a reduction in their wettability by molten steel. It is shown that the new oxide materials may be obtained in the production of tiles for the gate valves of steel-casting ladles.Translated from Ogneupory, No. 3, pp. 13–16, March, 1984.     

Some features of the production of thermal-shock-resistant cast corundum materials in ethyl silicate binders

Conclusions The use of ethyl silicate binders of an optimal composition makes it possible to produce cast corundum articles with a mullite-corundum binder with excellent characteristics.The best combination of properties is found in the articles when binders of optimal composition, close to stoichiometric, are used in the hydrolysis reaction of the ethyl silicate.The destruction and sintering processes in the corundum casts in an ethyl silicate binder during heat treatment are produced by the destruction kinetics of the hydrolysis products of the ethyl silicate and by the presence in them of active SiO₂. The sintering of articles of such a composition begins at 1100°C. The excellent thermal-shock resistance of the ceramic made from masses with ethyl silicate binders and the slower destruction of these ceramics result from the rational phase composition and structure of the material.Translated from Ogneupory, No. 2, pp. 35–39, February, 1982.     

Influence of Si species on intergrowth and anisotropic crystal growth of silicalite-1

Silicalite-1 crystals were hydrothermally synthesized from silica gels prepared under different conditions. The influence of the state of Si species in the silica gels and the concentrations of silicate ions and a template agent in the reaction sols on crystal growth of silicalite-1 was examined. The use of silica gels with a high degree of condensation of Si species resulted in the intergrowth of silicalite-1 crystals, whereas a low degree of condensation of Si species led to coffin-shaped crystals. Thus, the degree of condensation of Si species had significant influence on the intergrowth of silicalite-1 crystals. Moreover, at a low silicate concentration, silicalite-1 crystals elongated along the c-axis were obtained. With increasing silicate concentration in the reaction sols, the aspect ratio of silicalite-1 decreased. Furthermore, with decreasing the amount of N(C₃H₇) ₄ ⁺ used as a template agent, the silicalite-1 crystals became larger isotropically. Thus, the growth direction of silicalite-1 crystals was dependent on silicate ion concentration in the reaction sols, but not on N(C₃H₇) ₄ ⁺ concentration.     

Chloride-free biodegradable organic acid hydrolyzed zinc silicate coating

Partially hydrolyzed ethyl silicate has widely been used as a binder to formulate inorganic zinc silicate paint for anticorrosive coating applications. Hydrochloric acid is used most popularly to catalyze the hydrolysis of ethyl silicate. Although different acids have been tried as catalysts for ethyl silicate hydrolysis, no attempt has been made to make stable paints out of those hydrolyzed silicate binders. In this study, environment benign biodegradable organic acids such as oxalic acid, citric acid, lactic acid and acetic acid were used for the hydrolysis of ethyl silicate and compared with the hydrolysis using conventional hydrochloric acid. The hydrolyzed silicate sols were pigmented further with silica powder and evaluated for their stability. Of the various organic acids catalyst used, only oxalic acid catalyzed sol acted as a stable binder system. The pigmented binder was then mixed with metallic zinc to formulate anticorrosive inorganic zinc silicate paint. The resultant coatings were characterized for various physical, surface, mechanical and chemical resistance properties such as drying, hardness, adhesion (cross hatch) and solvent resistance. Corrosion resistance properties were analyzed by means of salt spray, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). The results revealed that the physical, mechanical, chemical and anticorrosive properties of the coating hydrolyzed with hydrochloric acid and oxalic acid are comparable. Thus, a chloride free biodegradable organic acid hydrolyzed inorganic zinc silicate primer is reported and due to its long term stability same also can be scaled up commercially.     

Microstructure and Phase Analysis of Ethyl Silicate-Bonded Alumina-Zircon Refractories

Alumina-zircon refractories are prepared using an aqueous ethyl silicate solution as the gel-polymerized bond. Test specimens are heat-treated by reaction sintering at different temperature (1450 – 1600°C) and holding times (1 – 4 h) to yield new refractory phases zirconium dioxide and mullite. The specimens are tested for strength, porosity, sintering shrinkage, apparent density, and chemical and phase composition using x-ray diffractometry and electron scanning microscopy. Reactive sintering is shown to be a effective route towards obtaining ethyl-silicate-bonded alumina-zircon refractories with tailored microscopic and physical properties. __________ Translated from Novye Ogneupory, No. 4, pp. 82 – 86, April, 2005.     

醇溶性无机富锌涂料的研制

醇溶性无机富锌涂料是以硅酸乙酯水解液为A组分,聚乙烯醇缩丁醛为B组分基料,配以锌粉以及其他填料、助刺、溶剂等制成。简要阐述了醇溶性富锌涂料成膜机理和对硅酸乙酯水解配方的研究,以及锌粉添加量对防腐性能的影响。     

Conductance studies on sodium silicates

Sodium silicate solutions with silicon dioxide: sodium monoxide mole ratios of 3.41 : 1 and 3.98 : 1 were dried to form gels. Some conductance studies were carried out on the sodium silicate as it dried, and when the dried material was heated up to 160 °C. The results suggest that conduction is mainly due to sodium ions both in the solution and in the gel; to this extent the mechanism of con, duction is similar to that in sodium silicate glasses. However, the gel has a much higher conductance than a glass of similar Na₂O : SiO₂ ratio, and this is probably because the gel contains hydroxyl ions and hydrated silicate ions, whereas the glass does not; moreover, the gel has a much less tightly packed structure than does the glass.     

硅酸盐基耐高温胶黏剂的研究现状及应用

硅酸盐胶黏剂具有耐温性好、环保无毒、工艺简单、成本低廉等优点,因而在耐火材料、耐酸胶泥、耐火涂料、铸造和模具等方面起着重要作用,近年来随着我国经济和各项事业的迅猛发展,耐高温无机胶黏剂的需求也越来越高。但是,粘结力低、耐水性差等缺陷制约了硅酸盐胶黏剂的推广应用。从物理改性和化学改性两方面详细地综述了硅酸盐胶黏剂的研究现状,并且以成本和可操作性作为考量指标,指出了众多改性途径中的最佳方案,此外对硅酸盐未来研究方向和应用前景作出展望。     

A Molecular Dynamic Study of Cementitious Calcium Silicate Hydrate (C–S–H) Gels

In this article, we study the polymerization of silicic acids (Si(OH)₄) in the presence of calcium ions by molecular dynamics simulations. We focus on the formation and structure of cementitious calcium silicate hydrate (C–S–H) gels. Our simulations confirm that, in accordance with experiments, a larger content of calcium ions slows down the polymerization of the cementitious silicate chains and prevents them from forming rings and three-dimensional structures. Furthermore, by an analysis of the connectivity of our simulated silicate chains and by a count of the number of Ca–OH and Si–OH bonds formed, the relationship with commonly used structural models of C–S–H gels, such as 1.4 nm tobermorite and jennite, is discussed.     

A new study on binder performance and formulation modification of anti-corrosive primer based on ethyl silicate resin

Zinc-rich ethyl silicate coatings are quite successful in protecting steel against corrosion under severe exposing conditions. In spite of providing excellent cathodic protection to steel structure after film curing, two-component zinc-rich ethyl silicate coatings have some limitations, one of which is inadequate shelf life as a result of in-can binder gelation.     

Solubility and Aging of Calcium Silicate Hydrates in Alkaline Solutions at 25°C

Calcium silicate hydrate (C-S-H) gels are the principal bonding material in portland cement. Their solubility properties have been described, enabling pH and solubilities to be predicted. However, the gels also interact with other components of cements, notably alkalis. C-S-H has been prepared from lime and silicic acid in solutions of sodium hydroxide or potassium hydroxide and by the hydration of tricalcium silicate (C₃S) in sodium hydroxide solutions. Analyses of aqueous phases in equilibrium with 85 gels show that the aqueous calcium and silicon concentrations fit smooth curves over the range of increasing sodium concentrations. Where anomalous data occur, they correspond to solids with low lime contents: such gels are tentatively assumed to fall into a region where the presence of another gel phase influences the aqueous composition. Dimensional changes have been observed in the hydration products of C₃S as a function of alkali content and these may be relevant to the alkali-silica reaction. The significance of this and other data is discussed with reference to real cement systems.     

Silica xerogels from rice hull ash: structure,density and mechanical strength as affected by gelation pH and silica concentration

Silica xerogels were produced from rice hull ash (RHA), and the structure, density and mechanical strength of the gels were investigated. Silica was extracted as sodium silicate from RHA using 1M NaOH. This silicate solution was concentrated by volume reduction and used to obtain silica concentrations of 0.04, 0.06, 0.08, 0.10, and 0.12 g cm⁻³. The pH values of these silicate solutions were adjusted to 9.0, 10.0, 10.5, or 11.0 to produce silica gels. The silica gels produced were then dried at 80 °C for 24 h. X‐ray diffraction demonstrated the amorphous nature of silica gels. Diffuse reflectance Fourier Transform Infrared (FTIR) spectroscopy was used to investigate the effect of gelation pH, and silica concentration on the chemical structure of the xerogel and concomitant effect on density and mechanical strength of the xerogel. The FTIR spectra demonstrated that at higher pH of gelation, siloxane bonding was the primary network in the xerogel. As the pH of gelation decreased, the structural silica gel network became the major interaction in the silica xerogel. At each gelation pH, the silica gel network increased with increase in silica concentration. The higher pH led to condensed glassy solids, while higher silica concentration produced highly porous silica xerogel. Hence, gelation pH and silica concentration of gel‐forming solution had significant effects on the density and the mechanical strength of xerogels produced from rice hull silica. © 2000 Society of Chemical Industry     

Elastic Properties of Porous Silica Derived from Colloidal Gels

The elastic properties were determined for gel-derived vitreous silica sintered from a relative density of 0.15 to full density. The gels were made from colloidal silica, potassium soluble silicate, and formamide. The soluble silicate was found to reinforce the gel network during gelation and its concentration relative to the colloidal silica affected Young's modulus for samples of relative density, 0.15 to 0.6 Young's modulus varied from 300 to 700 MPa at a relative density of 0.15 as a function of the soluble silicate concentration. Young's modulus at full density was measured to be 72.6 GPa. Poisson's ratio was found to be a function of relative density.